The present invention relates to a controlling device for a hydraulically operated cooling fan of construction equipment such as a bulldozer, hydraulic excavator, a wheel loader, and the like.
Generally, the use of cooling air blown from a cooling fan belt-driven by an engine is the widely used way of cooling the engine and a hydraulic equipment system of construction equipment. In this way, however, the rotational frequency of the cooling fan is proportional to the engine speed. Thus, cooling air is sent to a radiator and an oil cooler even when temperatures of engine cooling water, hydraulic oil, and the like do not reach a warming-up temperature appropriate for machine operation, for example, immediately after the starting of the engine. As a result, the cooling water and the hydraulic oil are supercooled, and more time is required for warming up.
As a prior art to settle the above disadvantage, a way of driving the cooling fan by means of an electric motor or a hydraulic motor the rotational frequency of which is controlled independently of engine rotation is known. As a prior art of a cooling system of construction equipment to which this way of cooling fan drive is applied, for example, a prior art disclosed in Japanese Patent Laid-open Bullctin No.10-68142 is given, and FIG. 13 shows a circuit diagram of a cooling system described in the above Bulletin.
In FIG. 13, a radiator 42a and an oil cooler 42b are disposed separately from an engine 41, and cooled by a cooling fan 45. The oil cooler 42b is disposed downstream of the radiator 42a with respect to air flow which arises during reverse rotation of the cooling fan 45. The cooling fan 45 is driven to stop, rotate normally, or rotate reversely by a hydraulic motor 48 controlled by a solenoid-controlled change-over valve 47 in a fan drive circuit 46. The solenoid-controlled change-over valve 47 is automatically switched by a controlling device 50 having an outside air temperature sensor 51, a cooling water temperature sensor 52, and a hydraulic oil temperature sensor 53. When all of an outside air temperature, a cooling water temperature, and a hydraulic oil temperature are lower than a set temperature at the starting of the engine, the controlling device 50 allows the rotation of the cooling fan 45 to remain stopped even if the engine 41 starts. Further, when the hydraulic oil temperature is lower than the set temperature although the cooling water temperature rises to the set temperature or more, the cooling fan 45 is reversed, whereby hydraulic oil in the oil cooler 42b is warmed up by warm air which has passed through the radiator 42a and dust which chokes the radiator 42a and the like is removed by against wind. Furthermore, when the cooling water temperature and the hydraulic oil temperature are not less than the set temperature, the cooling fan 45 is allowed to rotate normally to thereby cool cooling water and hydraulic oil.
It is described that as the result of the above, it becomes possible to shorten warming-up time of the hydraulic equipment and to improve cooling efficiency by removal of dust which chokes the radiator 42a and the oil cooler 42b. 
In the art disclosed in the aforesaid Japanese Patent Laid-open No.10-68142, however, there arise the following disadvantages.
Normal rotation, stop, and reverse rotation of the cooling fan 45 are controlled according to the cooling water temperature, the hydraulic oil temperature, and the outside air temperature. But, the aforesaid control is ON-OFF control, so that fine control can not be provided, and thereby optimum cooling efficiency is not obtained. Further, the cooling fan 45 is not controlled depending on the load of the engine 41. Hence, when the load of the engine 41 changes, the rotational frequency of the cooling fan 45 also changes, whereby cooling at optimum efficiency according to the cooling water temperature, the hydraulic oil temperature, and the outside air temperature can not be provided.
In view of the aforesaid disadvantages, an object of the present invention is to provide a controlling device for a hydraulically operated cooling fan capable of obtaining optimum cooling efficiency by continuously controlling a rotational frequency of the cooling fan according to a cooling water temperature, a hydraulic oil temperature, and an engine speed.
A first configuration of a controlling device for a hydraulically operated cooling fan according to the present invention is characterized in that
a controlling device for a hydraulically operated cooling fan in which a cooling system composed by forcedly cooling a radiator for cooling cooling water for an engine and an oil cooler for cooling, hydraulic oil for a hydraulic system by means of the cooling fan is provided independently of the engine, includes
a hydraulic motor for driving the cooling fan,
a variable displacement hydraulic pump capable of controlling a rotational frequency of the hydraulic motor,
a cooling water temperature sensor for detecting, a cooling water temperature,
a hydraulic oil temperature sensor for detecting a hydraulic oil temperature,
an engine speed sensor for detecting an engine speed, and
a controller which inputs detected signals from the cooling water temperature sensor, the hydraulic oil temperature sensor, and the engine speed sensor, computes and outputs a discharge capacity command value of the variable displacement hydraulic pump according to the inputted cooling water temperature, hydraulic oil temperature, and engine speed, and continuously controls a rotational frequency of the cooling fan by means of the variable displacement hydraulic pump.
According to the above configuration, the cooling fan rotational frequency is continuously controlled by the variable displacement hydraulic pump according to the cooling water temperature, the hydraulic oil temperature, and the engine speed, whereby the cooling fan rotational frequency is controlled smoothly without involving sharp change without being affected by rotational change of the engine. As a result, the cooling water temperature and the hydraulic oil temperature can be controlled finely, thus providing, optimum cooling efficiency.
The controlling device for the hydraulically operated cooling fan may have a configuration in which
the controller controls an upper limit of the cooling fan rotational frequency at a predetermined rotational frequency irrespective of changes in the engine speed when the engine speed is not less than a predetermined engine speed.
According to the above configuration, the upper limit of the cooling fan rotational frequency is controlled at the predetermined rotational frequency irrespective of changes in the engine speed when the engine speed is not less than the predetermined engine speed. Accordingly, since the rotational frequency of the cooling fan is almost constant even if engine load increases and thereby the engine speed decreases, cooling capacity does not lower. Moreover, the rotational frequency of the cooling fan is almost constant even if the engine load decreases and thereby the engine speed increases, thereby not causing supercooling and unnecessary consumption of energy, which enables efficient cooling. Generally, as for the cooling fan, when the rotational frequency thereof exceeds some rotational frequency level, a produced sound abruptly increases, but an increase in cooling capacity corresponding to an increase in fan drive energy is not given. Meanwhile, according to the configuration of the present invention, the rotation of the fan at excessively high speed such as described above can be avoided, thus enabling efficient cooling from the viewpoint of noise reduction of the cooling fan and fan drive energy, and further serving the prevention of breakage of the cooling fan.
Further, the controlling device for the hydraulically operated cooling fan may have a configuration in which
the upper limit of the cooling fan rotational frequency is set according to the cooling water temperature and the hydraulic oil temperature.
Owing to the above configuration, the cooling fan is driven at a nearly constant rotational frequency based on the cooling water temperature and the hydraulic oil temperature, irrespective of changes in the engine speed. Therefore, without causing insufficient cooling or supercooling, efficient cooling becomes possible.
Furthermore, the controlling device for the hydraulically operated cooling fan may have a configuration in which
the controller controls the cooling fan rotational frequency at a predetermined low speed rotational frequency when the cooling water temperature and the hydraulic oil temperature are not more than a predetermined low temperature.
According to the above configuration, when the cooling water temperature and the hydraulic oil temperature are not more than the predetermined low temperature, the cooling fan rotational frequency is controlled at the predetermined low speed rotational frequency which is at the level of no cooling capacity. Thus, a very small amount of hydraulic oil is always circulated in the oil cooler in the state of the low temperature, thereby preventing supercooling of the temperature of the hydraulic oil. Further, the hydraulic pump for the cooling fan discharges and circulates a small amount of oil, thereby preventing the pump from overheating and seizing up.
A second configuration of a controlling device for a hydraulically operated cooling fan according to the present invention is characterized in that
a controlling device for a hydraulically operated cooling fan in which a cooling system composed by forcedly cooling a radiator for cooling cooling water for an engine and an oil cooler for cooling hydraulic oil for a hydraulic system by means of the cooling fan is provided independently of the engine, includes
a hydraulic motor for driving the cooling fan,
a variable displacement hydraulic pump capable of controlling a rotational frequency of the hydraulic motor,
a limit switch for setting an upper limit rotational frequency of the cooling fan, and
a controller which inputs a signal from the limit switch, outputs a command value to limit a discharge capacity of the variable displacement hydraulic pump to not more than a predetermined value when the inputted signal is a limit signal, and controls a rotational frequency of the cooling fan at not more than a predetermined limited rotational frequency.
According to the above configuration, the rotational frequency of the cooling fan can be controlled at not more than the predetermined limited rotational frequency by the limit switch, thereby reducing the upper limit rotational frequency of the cooling fan as the occasion demands in the case of operations in a city area, which makes it possible to reduce noise to comply with the request of a working site and to easily cope with noise regulation. Moreover, engine output to the cooling fan can be limited by the limit switch, whereby engine output can be effectively utilized for the vehicle body and the working machine according to the load of the engine.
A third configuration of a controlling device for a hydraulically operated cooling fan according to the present invention is characterized in that
a controlling device for a hydraulically operated cooling fan in which a cooling system composed by forcedly cooling a radiator for cooling cooling water for an engine and an oil cooler for cooling hydraulic oil for a hydraulic system by means of the cooling fan is provided independently of the engine, includes
a hydraulic motor for driving the cooling fan,
a hydraulic pump for driving the hydraulic motor,
a cooling water temperature sensor for detecting a cooling water temperature,
a hydraulic oil temperature sensor for detecting a hydraulic oil temperature,
an engine speed sensor for detecting an engine speed, and
a controller which inputs detected signals from the cooling water temperature sensor, the hydraulic oil temperature sensor, and the engine speed sensor, computes an upper limit value of a rotational frequency of the cooling fan based on the inputted detected signals, and controls the rotational frequency of the cooling fan by the computed upper limit value.
According to the above configuration, the upper limit value of the rotational frequency of the cooling fan is set according to the cooling water temperature, the hydraulic oil temperature, and the engine speed, and the cooling fan rotational frequency is controlled based on the upper limit value via the hydraulic motor, whereby the cooling fan rotational frequency is controlled continuously without being affected by rotational change of the engine and without involving sharp change. As a result, the cooling water temperature and the hydraulic oil temperature can be controlled finely, thus providing optimum cooling efficiency. Moreover, since the upper limit value of the cooling fan rotational frequency is set according to the cooling water temperature and the hydraulic oil temperature, the cooling fan is driven at an almost constant rotational frequency based on the cooling water temperature and the hydraulic oil temperature, irrespective of changes in engine speed. Consequently, without causing insufficient cooling or supercooling, efficient cooling becomes possible.